Cover crop research points to benefits that go beyond soil health

By Keena Lykins

The benefits of using cover crops are usually subtle, but Terry Taylor of Geff, Ill., saw firsthand the difference they made this year. While he watched his corn fields that weren’t preceded with cover crops dry up after six weeks with no rain, his other corn held on.

"Cover crops increase a soil’s physical properties and improve nutrient cycling," he says. "That translates into increased water-holding capacity and, in a year like this, the ability to tolerate dry weather for longer periods."

Taylor has used cover crops to protect his soil for three decades. Ten years ago, he and Mike Plummer, former University of Illinois Extension specialist, developed a cover crop strategy to rebuild the soil organic matter in his fields. He estimates he uses cover crops on 80% of the 2,000 acres he farms.

More research needed. Although farmers have long used cover crops to guard against erosion and nutrient losses, their full potential remains unknown and underfunded, says Tom Kaspar, plant physiologist at the USDA–Agricultural Research Service (ARS) National Laboratory for Agriculture and the Environment in Ames, Iowa, and a collaborator with the Department of Agronomy at Iowa State University.

Growers and researchers often have the attitude that we already know all we need to know about cover crops, he says, but there are a lot of variables that should be explored, such as breeding better cover crop varieties for the Upper Midwest.

"Even limited research in breeding or management could result in significant improvements in how well cover crops work in corn-soybean rotations," he says. Current research studies suggest that cover crops also offer potential pest and disease suppression benefits, he adds.

Other researchers are finding similar results. In Michigan, a study on seeding cover crop seed mixed into manure slurry looks promising. In the study, liquid manure and seeds are applied with
manure applicators that fracture no-till ground enough for the seeds to have a protected place to germinate. The practice could provide an economic boost to farmers, says Tim Harrigan of the Department of Biosystems and Agricultural Engineering at the University of Michigan.

"We had not only yield benefits, but also suppression of natural pests," he explains. "We calculated that the system saves growers 2 gal. of fuel and a half-hour in labor costs per acre."

Disease fighters. Plummer’s research in Illinois has yielded similar suppressive benefits. "We’re studying cover crops’ influences on diseases, especially in soybeans," says Plummer, who now works as an independent consultant. "We’re in the second year of research, but initial research shows a significant reduction in sudden death syndrome [SDS] and soybean cyst nematodes."

In one study, in fields where many of the plants were infected with SDS, covers of mustard or rape significantly reduced the loss. That study is moving into more locations, and preliminary results are "looking really good," Plummer says.

The news that cereal rye helps suppress marestail was well accepted, and farmers planted so much that there was a shortage of cereal rye seed in the fall of 2011. Plummer says that is encouraging, but still less than 1% of growers use cover crops.

"Most growers are afraid of them," he says. "They don’t know what to do with a green growing crop in the spring. We need to break our customary habits to get the full benefits of cover crops."